Download Pathogenesis of infectious disease

Pathogenesis of infectious
disease
• Path means disease
• Pathogens refer to microorganism capable to
cause a disease.
• Pathology : the study of structural and
functional manifestation of disease.
• Pathologist : a physician who has specialized
in pathology.
• Pathogenicity : the ability to cause a disease
• Pathogenesis : is the step or mechanisms
involved in development of a disease
• Phs in the corse of an infectious disease:
1. Incubation period: is the time that elapses
between arrival of the pathogens and the onset
of symptoms. And it is varies by many factor as
health state-virulence of the pathogens- number
of pathogens that enter the body.
2. Prodormal period: is the time during which
patient feels out of sorts but not yet
experiencing actual symptoms of the disease.
3. Period of illness: is the time during which the
patient experiences the typical symptoms
associated with that particular disease
.(headache – sore throat-sinus congestion)
• The convalescent period: is the time during which the
patient recover.
• Localized infection
• Systemic infection
• Acute infection : rapid infection followed out by rapid
recovery (measles-mumps-influenza)
• Chronic infection : slow insidious and last for long time
• Symptoms of a disease: define as some evidence of a
disease that is experienced by the patients.
( headache-fever-pain-itching)
• Asymptomatic disease
• Sign of a disease: define as some objective evidence of
a disease that is experienced by the patients. (skin
rash-enlargment of the spleen)
Latent infection : an old infection that was
contained by the body but may re-activate at
any time as ( ?)
Primary infection: is the infection that the body
get exposed to for the first time .
Secondary infection : is an infection that follows
a primary infection.
• Step in the pathogenesis of infections
disease:
1. Entry: of the pathogen into the body by:
(Penetration, inhalation, ingestion and
introduction of the pathogens directly into the
blood. [shades needles]
2. Attachment: of the pathogen to some tissues
within the body.
3. Multiplication: with local or system
4. Invasive / spread of the pathogens
5. Evasion of a host defenses.
6. Damage to host tissue (s). extensive or death.
• Virulence:
• is measure or degree of pathogenecitiy.
different organism vary in their ability to cause
disease some strain virulence some is a
virulence.
• Virulence factor: are the phenotypic
characteristics of a microorganism that enable
it to cause disease.
1. Structural features as pili ,capsule, flagella. It
help adhesion: which is molecule on the surface
of the pathogens that able to recognize the
reception on the host cell: that is glycoprotein
molecule on the surface of the host cell that the
adhesion on the pathogen attach to it.
2. Obligate intracellular pathogens.
3. Facultative intracellular pathogens.
4. Capsules: antiphagocytic by WBC. (No receptor).
5. Flagella: move and invade the aqueous area in
the body it avoid phagocytosis.
6. Exoenzymes : is the two major virulence factors by
which bacteria cause disease the exoenzyme as
(a) coagulase as in staphaurus: clot plasma → sticky
coat → protect it from phagocytes.
(b) kinases: → streptococcus & stophausus: body
produce fibricolt → kinases → lysis.
(c) hyaluronidase: enable organism to spread through
connective tissue by breaking down hyaluronic acid.
(d) collagenase: Break down the collagen to invade
tissue.
(e) hemolysins: damage RBC.
(f) lecithinase: damage extensive area of tissue.
7. Toxins: there are endotoxins that is integral
part of the cell wall of the gram-negative
bacteria can cause a number of adverse
physiologic effect.
Exotoxins are the toxins that produced
within the cells and then releases from the
cell example:
– Neurotoxins= that cause paralysis.
– Enterotoxins = gastro intestinal disease.
• Mechanisms by which pathogens escape
immune responses:
• The pathogens change their surface antigens
example: influenze virus, HIV and nisseria.
• The pathogen's surface antigens closely
resemble host antigens and therefore not
recognized by immune system = molecular
mimicry.
• Destruction of the host antibodies by
producing enzyme as (IgA protease) that
destroy IgA.